Electrochemical cell

Abstract

An electrochemical cell comprises as an anode, a lithium transition metal oxide or sulphide compound which has a [B 2 ]X 4 n− spinel-type framework structure of an A[B 2 ]X 4 spinel wherein A and B are metal cations selected from Li, Ti, V, Mn, Fe and Co, X is oxygen or sulphur, and n− refers to the overall charge of the structural unit [B 2 ]X 4 of the framework structure. The transition metal cation in the fully discharged state has a mean oxidation state greater than +3 for Ti, +3 for V, +3,5 for Mn, +2 for Fe and +2 for Co. The cell includes as a cathode, a lithium metal oxide or sulphide compound. An electrically insulative lithium containing liquid or polymeric electronically conductive electrolyte is provided between the anode and the cathode.

1. An electrochemical cell, comprising
 as at least part of an anode, a lithium transition metal oxide compound which has a [B 2 ]X 4   n−  spinel-type framework structure of an A[B 2 ]X 4  stochiometric spinel or defect spinel wherein A comprises Li, B comprises Li and Ti, X is oxygen (O), and n− refers to the overall charge of the structural unit [B 2 ]X 4  of the framework structure, and the transition metal cation of which in the fully discharged state of the cell has a mean oxidation state greater than +3 for Ti, and further wherein the anode is further defined as comprising Li 4 Ti 5 O 12 , which can be written as (Li) 8a [Li 0.33 Ti 1.67 ] 16d O 4  in ideal spinel notation; 
 as at least part of a cathode, a lithium metal oxide compound having a stochiometric spinel or defect spinel structure, any such a spinel structure having, as its basic structural unit, a unit of the formula [B 2 ]X 4   n− , where [B 2 ]X 4   n−  is the structural unit of an A[B 2 ]X 4  spinel, with the X anions being arranged to form a negatively charged anion array, and wherein
 A comprises a lithium cation; 
 B comprises at least two metal cations, of which one is manganese and the other is not manganese; 
 X is oxygen (O); and 
 n− refers to the overall charge of the structural unit [B 2 ]X 4  of the framework structure, with the transition metal cations of the anode being more electropositive than those of the cathode; and 
 
 an electrically insulative, lithium containing, liquid or polymeric, ionically conductive electrolyte between the anode and the cathode, such that, on discharging the cell, lithium ions are extracted from the spinel-type framework structure of the anode, with the oxidation state of the metal ions of the anode thereby increasing, while a concomitant insertion of lithium ions into the compound of the cathode takes place, with the oxidation state of the metal ions of the cathode decreasing correspondingly. 
 
     
     
       2. The electrochemical cell of  claim 1 , wherein the [B 2 ]X 4  framework structure of the cathode contains, within the framework structure or within interstitial spaces present in the framework structure, additional metal cations to the lithium ions and the other A and B cations, with the additional metal cations being present in an amount less than 10 atomic percent. 
     
     
       3. The electrochemical cell of  claim 1 , wherein, in the compound of the anode, the [B 2 ]X 4  framework structure contains, within the framework structure or within interstitial spaces present in the framework structure, additional metal cations to the lithium ions and the other A and B cations, with the additional metal cations being present in an amount less than 10 atomic percent. 
     
     
       4. The electrochemical cell of  claim 1 , wherein the compound of the cathode is Li 1+δ Mn 2−δ O 4  where 0 <δ≦0.1. 
     
     
       5. The electrochemical cell of  claim 1 , wherein the compound of the cathode is LiM δ/2 Mn 2−δ O 4  where M=Mg or Zn and 0<δ≦0.05. 
     
     
       6. The electrochemical cell of  claim 1 , wherein the electrolyte is a room temperature electrolyte selected from the group consisting of LiClO 4 , LiBF 4 , and LiPF 6  dissolved in an organic solvent selected from the group consisting of propylene carbonate, ethylene carbonate, dimethyl carbonate, dimethoxyethane and mixtures thereof. 
     
     
       7. The electrochemical cell of  claim 1 , wherein the electrolyte is a polymeric electrolyte selected from the group consisting of polyethylene oxide (PEO)—LiClO 4 , PEO—LiSO 3 CF 3,  and PEO—LiN(CF 3 SO 2 ) 2 . 
     
     
       8. The electrochemical cell of  claim 4  where δ=0.03.